Scientific theories behind the origins of sea salt started with Sir Edmond Halley in 1715, who proposed that salt and other minerals were carried into the sea by rivers, leached out of the ground by rain runoff. Seawater through the process of evaporation creates clouds which replenished rivers and streams with rain: the salt is not capable of evaporation, leaving oceans with a high level of salinity. Halley noted that of the small number of lakes in the world without ocean outlets, such as the Dead Sea and the Caspian Sea, have very high salinity levels. Halley called this process "continental weathering".

Halley's theory is partly correct: in addition, sodium was leached out of the ocean floor when the oceans were first formed. The presence of the other element of salt, chlorine results from "outgassing" of chlorine and other gases from the earth's core[?] via volcanoes and undersea vents[?]. The sodium and chlorine subsequently combined to form sea salt.

Ocean salinity has been stable for millions of years, most likely as a consequence of a chemical/tectonic system which recycles the salt. Since the ocean's creation, sodium is no longer leached out of the ocean floor, but instead is forming sedimentary layers[?] on the ocean beds. One theory is that plate tectonics result in the salt being forced under the land masses, where it is again leached to the surface.

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